The present invention is directed to a process for preparing toners. More specifically, the present invention is directed to a process for preparing toners comprising a resin, a pigment, and a charge control additive, wherein the charge control additive is premixed with the pigment in the absence of a solvent, the mixture is introduced into an extruder and extruded, the resin is subsequently added to the extruder at a port downstream of the port used for introduction of the pigment-charge control additive mixture, and the resulting composition is extruded in the extruder.
Utilization of the extrusion process to prepare toner compositions is known. Extrusion is a continuous process that generally entails dry blending the toner ingredients, placing them into an extruder, melting and mixing the mixture, extruding the material, and reducing the extruded material to pellet form. The pellets are further reduced in size by grinding or jetting, and are then classified by particle size. A typical extrusion apparatus and process are described in copending application U.S. Ser. No. 535,517/83, the disclosure of which is totally incorporated herein by reference. Other known methods of preparing toners include melt blending in a Banbury apparatus, spray drying, dispersion polymerization, solution polymerization, and the like. The extrusion process possesses a number of advantages not present for the Banbury process in that, for example, extrusion is a continuous process rather than a batch process, and in that the extrusion process is more suitable to automation, which allows for more economical operation.
A vent type extruder for extrusion molding of a kind or kinds of resin materials mixed or not mixed with other raw material is disclosed in U.S. Pat. No. 4,110,844. This extruder comprises a heating cylinder with a plurality of ventages formed in open-mouthed relation, with the effective length of an extruding screw to the diameter of the screw at the predetermined ratio of over thirty to one having a range within which resin materials containing a large quantity of moisture and gas may be completely dried up through a single extruding operation without previously appealing to a desiccating treatment. The disclosure of this patent is totally incorporated herein by reference.
British Pat. No. 1,037,547 discloses a process for continuous, homogeneous incorporation into plastics melts of substances to be finely dispersed therein. The process entails introducing into an extruder a metered stream of, for example, a dye concentrate at the first feed inlet, introducing a molten stream of plastic containing volatile constituents at the second feed inlet, and passing the resulting mixture through a degassing chamber. Subsequent to degassing, additional liquid components are introduced into the mixture and homogeneously dispersed therein.
Further, U.S. Pat. No. 4,649,005 discloses a method for preparing filled silicone rubber bases without plasticizer by passing all of the filler together with from 30 to 100 percent of the total weight of the polyorganosiloxane ingredient of the base through the first kneading section of a compounding extruder and adding any remaining polyorganosiloxane before passing the composition through a second kneading section of the compounding extruder. The two kneading sections are maintained at temperatures of from 200.degree. to 300.degree. C. The disclosure of this patent is totally incorporated herein by reference.
In addition, U.S. Pat. No. 4,621,039 discloses a toner composition comprising resin particles and pigment particles surface treated with amine or ammonium salt charge enhancing additives, wherein the charge enhancing additives are associated with the pigment particles and are present as a continuous coating on the pigment particles. This association of the charge enhancing additives with the pigment particles is effected by mixing the pigment particles and the charge enhancing additives prior to adding the resulting mixture to the polymer resin particles, as set forth in column 6, lines 56 et seq., and results in a toner composition enabling rapid admix times. The process entails treating the pigment particles with a solution of the charge enhancing additive dissolved in a suitable solvent, and subsequently removing the solvent, thereby resulting in pigment particles with permanently attached charge control additives, as set forth at columns 6 and 7, bridging paragraph. In contrast, the present invention entails premixing of the charge control additive and the pigment particles in the absence of a solvent.
Copending application U.S. Ser. No. 630,797, entitled "Process and Apparatus for Preparing Toner Particles," the disclosure of which is totally incorporated herein by reference, discloses an apparatus for lowering the melt temperature of a toner formulation which comprises, in operative relationship, a toner processing apparatus and a means for injecting liquid components therein. Also disclosed in this application is a process for lowering the melt temperature of a toner formulation, generally by from about 10.degree. F. to about 60.degree. F., which comprises providing a toner processing apparatus, adding thereto toner resin particles and pigment particles, mixing and melting the particles, and injecting into the formulation components with a boiling point lower than the melting temperature of the resin particles, thereby enabling more effective dispersion of the pigment particles in the other toner components. The disclosure of this application is totally incorporated herein by reference.
Although known processes for preparing electrophotographic toners are suitable for their intended purposes, a need continues to exist for processes for preparing toners. More specifically, a need exists for improved processes for preparing electrophotographic toners by an extrusion process wherein the resulting toner may be charged to triboelectric levels exceeding the triboelectric charging values of toners of the same composition that have been prepared by known extrusion processes. A need also exists for toner preparation processes that mix the pigment and the charge control additive prior to being mixed with the toner resin, thereby allowing the charge control additive and the pigment to undergo a significant amount of interaction. Further, there is a need for toner preparation processes that can be carried out in a standard extruder, with no need to modify the extruder, and that also produces toner that may be charged to higher triboelectric levels than toners of the same composition that have been prepared by conventional extrusion processes. In addition, a need exists for simple and economical methods of preparing electrophotographic toners. There is also a need for a method of preparing toners wherein the pigment and the charge control additive are permitted to interact in the absence of a solvent, enabling interaction between the pigment and charge control additive.